Drinking flask



FIG. 1 is a top right perspective view of a drinking flask showing my new design.

FIG. 2 is a front elevational view of the design.

FIG. 3 is a right side elevational view of the design.

FIG. 4 is a left side elevational view of the design.

FIG. 5 is a top plan view of the design; and,

FIG. 6 is a bottom plan view of the design. 

The ornamental design for a drinking flask, as shown and described. 